Aboveground decomposition dynamics in riparian depression and slope wetlands of central Pennsylvania

We examined two types of groundwater-fed wetlands (riparian depressions and slopes) classified using the hydrogeomorphic (HGM) system. These wetland types had previously been shown to differ hydrologically. Our first objective was to determine if HGM was a useful structuring variable when examining aboveground decomposition dynamics (rate of mass loss and rate of nitrogen loss). Our second objective was to determine what soil variables were related to any differences in aboveground decomposition dynamics we might find regardless of HGM subclass. We used the litterbag field bioassay technique, and employed a standard litter type (Phalaris arundinacea) across all wetlands. Our results indicated that HGM would not readily serve as an adequate structuring variable for aboveground decomposition in riparian depressions and slope wetlands of central Pennsylvania. Discriminant analysis and classification and regression tree (CART) modeling found soil cation exchange capacity, soil pH, soil organic matter, and soil % nitrogen to be potentially important soil variables related to mass loss, and soil % nitrogen and soil pH to be potentially important variables related to nitrogen loss rate.     

Developing an index of wetland condition from ecological data: An example using HGM functional variables from the Nanticoke watershed,USA

Demand for data on the ecological condition of wetlands is increasing as state and federal management programs recognize its value in reporting on the ambient condition of the resource, targeting restoration and protection efforts, evaluating the effects of mitigation and restoration practices, supporting regulatory decisions, and tracking the impact of land use decisions. We developed an approach for generating a single measure of wetland condition from ecological variables used in hydrogeomorphic (HGM) assessment. An Index of Wetland Condition (IWC) was developed from HGM field data collected to assess freshwater, non-tidal flat, riverine, and depression wetlands in the Nanticoke River watershed. The HGM variables were screened and scored based on a range check, responsiveness, and metric redundancy, employing a method used to develop indices of biotic integrity. Weights of the individual variables were adjusted to reflect our understanding of wetland ecology and to include variables that represented the vegetation, hydrology, and buffer of a wetland. The final IWC score discriminated high, medium, and low site disturbance classes in flat and riverine wetlands and high and low disturbance classes in depressions, one-way ANOVA F-values ranged from 44.5 to 79.1 (all p <0.0001). The combination of the IWC and HGM assessments provides a comprehensive evaluation of the wetland resource. HGM produces information on specific wetland functions. The IWC concisely conveys the ecological condition of the resource and maximizes the utility of the data collected in an HGM assessment.     

Hydrogeomorphology,environment, and vegetation associations across a latitudinal gradient in highland wetlands of the northeastern USA

Undisturbed, highland wetlands in the northeastern USA are unique habitats which maintain ecological integrity in this region. These ecosystems may be threatened by a changing environment. To protect, restore, and create these wetlands, an understanding of the relationship between vegetation composition, environmental regime, and the underlying hydrogeomorphology is needed. Using a hydrogeomorphic (HGM) classification scheme, we analyzed the environmental regime and vegetation in groundwater and small-order, stream-fed wetlands in the Adirondacks and Catskills of New York, the Appalachians of Pennsylvania and of Virginia and West Virginia. The similarity of environmental regime and then species composition between wetlands across and within regions were analyzed using ordination and cluster analysis. Plant associations and distinguishing factors were determined. Within a region, wetlands with similar environmental regime or species composition were often grouped by HGM subclass. Beaver influence and groundwater sources may account for discrepancies between HGM and community composition. Similarly structured plant associations across regions included Acer/herbaceous wetlands, Acer/Fraxinus slopes, and Acer/Tsuga/herbaceous wetlands. Plant associations were primarily distinguished by soils in the Adirondacks, soils and hydrology in the Catskills, spatial location and disturbance in Pennsylvania, and spatial location in Virginia. Regional differences and non-environmental drivers of species composition will modify generalized relationships between hydrogeomorphology, environmental regime, and species composition and should be accounted for in wetland design and management activities.     

Developing a wetland-type classification system in the Republic of Korea

Though there are wetlands listed by the IUCN and wetland protection areas designated by the government, it is presumed that there would be more wetlands in Korea when they are surveyed and classified according to international wetland criteria, but a considerable amount of area is yet to be identified. Therefore, in order to conduct a systematic status survey on the wetlands of Korea, a wetland classification system needs to be developed first. The objectives of this paper include reviewing international wetland classifications and mapping systems of the USA, Germany, the Netherlands, Japan and North Korea and developing a wetland classification and mapping system appropriate to Korea based on an understanding of the major case examples of wetland types. Then, the developed system was applied to the Phanmun field watershed located at the western DMZ in Korea to conduct a case study. The overall process of a wetland classification and mapping system developed in this study is undertaken as the following from step 1 to step 5. First, wetlands are identified based on three parameters: hydrology, hydrophytes and hydric soil. Second, wetland delineation distinguished wetland areas and non-wetland areas by identifying wetlands through a field survey. Third, an ecological survey is conducted in order to classify wetland characteristics and types for the target area. Ecological survey items include the topography, landscape, biota, pollutant sources and land use status. Fourth, a wetland classification is developed through a hybrid approach based on HGM (the hydrogeomorphic method). Level 1 is classified into inland, estuarine and costal areas. Level 2, the target area, is classified as an eco-region at a watershed level, and level 3 is classified into depression, riverine, slope, flat and fringe areas based on a HGM approach. Level 4 is classified into detailed wetland types based on specific characteristics of wetlands. Level 5 is classified into marsh and swamp based on grasslands and shrubs and forest trees. Level 6 indicates the dominant vegetation communities.

Removal of Dibenzofuran, Dibenzo-p-Dioxin, and 2-Chlorodibenzo-p-Dioxin from Soils Inoculated with Sphingomonas sp. Strain RW1

Removal of dibenzofuran, dibenzo-p-dioxin, and 2-chlorodibenzo-p-dioxin (2-CDD) (10 ppm each) from soil microcosms to final concentrations in the parts-per-billion range was affected by the addition of Sphingomonas sp. strain RW1. Rates and extents of removal were influenced by the density of RW1 organisms. For 2-CDD, the rate of removal was dependent on the content of soil organic matter (SOM), with half-life values ranging from 5.8 h (0% SOM) to 26.3 h (5.5% SOM).     

Removal of dibenzofuran, dibenzo-p-dioxin, and 2-chlorodibenzo-p-dioxin from soils inoculated with Sphingomonas sp. strain RW1

Removal of dibenzofuran, dibenzo-p-dioxin, and 2-chlorodibenzo-p-dioxin (2-CDD) (10 ppm each) from soil microcosms to final concentrations in the parts-per-billion range was affected by the addition of Sphingomonas sp. strain RW1. Rates and extents of removal were influenced by the density of RW1 organisms. For 2-CDD, the rate of removal was dependent on the content of soil organic matter (SOM), with half-life values ranging from 5.8 h (0% SOM) to 26.3 h (5.5% SOM).     

Comparing carbon sequestration in temperate freshwater wetland communities

High productivity and waterlogged conditions make many freshwater wetlands significant carbon sinks. Most wetland carbon studies focus on boreal peatlands, however, with less attention paid to other climates and to the effects of hydrogeomorphic settings and the importance of wetland vegetation communities on carbon sequestration. This study compares six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: an isolated depressional wetland site connected to the groundwater table, and a riverine flow‐through wetland site that receives water from an agricultural watershed. Three cores were extracted in each community and analyzed for total carbon content to determine the soil carbon pool. Sequestration rates were determined by radiometric dating with ¹³⁷Cs and ²¹⁰Pb on a set of composite cores extracted in each of the six communities. Cores were also extracted in uplands adjacent to the wetlands at each site. Wetland communities had accretion rates ranging from 3.0 to 6.2 mm yr^?1. The depressional wetland sites had higher (P < 0.001) organic content (146 ± 4.2 gC kg^?1) and lower (P < 0.001) bulk density (0.55 ± 0.01 Mg m^?3) than the riverine ones (50.1 ± 6.9 gC kg^?1 and 0.74 ± 0.06 Mg m^?3). The soil carbon was 98–99% organic in the isolated depressional wetland communities and 85–98% organic in the riverine ones. The depressional wetland communities sequestered 317 ± 93 gC m^?2 yr^?1, more (P < 0.01) than the riverine communities that sequestered 140 ± 16 gC m^?2 yr^?1. The highest sequestration rate was found in the Quercus palustris forested wetland community (473 gC m^?2 yr^?1), while the wetland community dominated by water lotus (Nelumbo lutea) was the most efficient of the riverine communities, sequestering 160 gC m^?2 yr^?1. These differences in sequestration suggest the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets.     

The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.

1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers. 2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south-eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers. 3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority. 4. The HGM approach also provides a framework for long-term monitoring of mitigation success or failure and, if failing, a focus on topical remediation. 5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.     

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (D_b), total carbon (C_t), nitrogen (N_t), and phosphorus (P_t), extractable phosphate (PO_4w), nitrogen (N_ex), and cations (Ca_ex, Mg_ex, K_ex, Na_ex), as well as pH. Bulk density, P_t, Ca_ex, Mg_ex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.     

Effects of wheel running on photoperiodic responses of Djungarian hamsters (Phodopus sungorus)

Djungarian hamsters (Phodopus sungorus) were exposed to artificial short days either with access to a running wheel (RW) or without. Within 6 weeks RW hamsters considerably increased their body mass, whereas controls showed the typical body mass reduction. Estimation of paired testis weights indicated a decelerated testis regression in RW hamsters. Subsequent locking of RWs for 9 weeks led to a decline in body mass of RW animals in parallel to controls. Daily torpor was almost completely missing in hamsters with initially unlocked wheels. During the final phase when RWs were again unlocked (3 weeks), body mass of exercising hamsters increased again, while controls reached the nadir in body mass. In comparison to equiponderate long-day (LD) controls the relative liver weight of RW hamsters was significantly increased unlike the relative heart weight. However, the latter tended to be higher than in sedentary LD hamsters. A growth-stimulating effect of wheel running was proven by elongated femora in exercising short-day (SD) hamsters compared to SD controls and suggested by exercise-induced elevation of body mass in a further experiment under continuous LD conditions, indicating a growth-promoting effect of wheel running independent from the photoperiod.     

Hydrologic, Edaphic, and Vegetative Responses to Microtopographic Reestablishment in a Restored Wetland

Microtopography is a characteristic feature of many natural wetlands that is commonly lacking in restored wetlands (RWs). Consequently, it has been suggested that microtopography must be reestablished in RWs to accelerate the development of wetland function. The objective of this research was to examine responses of hydrology, soils, and vegetation to microtopographic reestablishment at a 3‐year‐old RW site in North Carolina. Microtopography was reestablished by configuring hummocks (mounds) and hollows (depressions), on otherwise level terrain (flats) of intermediate elevation. For most of the 2003 growing season, mean water table depths were below the soil surface in the flats and 10 cm above the soil surface in the hollows. Analysis of variance revealed significant microtopography by time interactions for soil temperature (p < 0.05) and moisture (p < 0.001), indicating that differences between zones were not consistent throughout the growing season. Hummocks had significantly higher nitrate (p < 0.0001) and ammonium (p= 0.001) than flats and hollows for most of the growing season. Differences in microbial biomass carbon and denitrification enzyme activity across the microtopographic zones were not detected. Plant species richness was significantly different (p < 0.001) across the microtopographic zones, with hummocks < hollows < flats. Flats supported the greatest numbers of wetland species. Aboveground biomass differed significantly (p < 0.001) across the microtopographic zones and followed a different pattern than richness: hummocks < flats < hollows, owing to the growth of emergent wetland herbs in hollows.     

Connecting carbon and nitrogen storage in rural wetland soil to groundwater abstraction for urban water supply

We investigated whether groundwater abstraction for urban water supply diminishes the storage of carbon (C), nitrogen (N), and organic matter in the soil of rural wetlands. Wetland soil organic matter (SOM) benefits air and water quality by sequestering large masses of C and N. Yet, the accumulation of wetland SOM depends on soil inundation, so we hypothesized that groundwater abstraction would diminish stocks of SOM, C, and N in wetland soils. Predictions of this hypothesis were tested in two types of subtropical, depressional‐basin wetland: forested swamps and herbaceous‐vegetation marshes. In west‐central Florida, >650 ML groundwater day^?1 are abstracted for use primarily in the Tampa Bay metropolis. At higher abstraction volumes, water tables were lower and wetlands had shorter hydroperiods (less time inundated). In turn, wetlands with shorter hydroperiods had 50–60% less SOM, C, and N per kg soil. In swamps, SOM loss caused soil bulk density to double, so areal soil C and N storage per m² through 30.5 cm depth was diminished by 25–30% in short‐hydroperiod swamps. In herbaceous‐vegetation marshes, short hydroperiods caused a sharper decline in N than in C. Soil organic matter, C, and N pools were not correlated with soil texture or with wetland draining‐reflooding frequency. Many years of shortened hydroperiod were probably required to diminish soil organic matter, C, and N pools by the magnitudes we observed. This diminution might have occurred decades ago, but could be maintained contemporarily by the failure each year of chronically drained soils to retain new organic matter inputs. In sum, our study attributes the contraction of hydroperiod and loss of soil organic matter, C, and N from rural wetlands to groundwater abstraction performed largely for urban water supply, revealing teleconnections between rural ecosystem change and urban resource demand.     

Landscape hydrogeomorphic conditions determine structure and species composition of an ephemeral floodplain wetland

Wetlands are major sources of habitat heterogeneity, with certain environmental variables controlling wetland structure and composition. There is very little information on the heterogeneity of ephemeral floodplain wetland patch mosaics and how hydrogeomorphic circumstance affects composition and structure. Structure (wetland size) and composition (herbaceous species) are two attributes of an ephemeral wetland that are easily quantifiable using a moving window analysis. The moving window analysis is a statistical technique that identifies significant changes in parameters (i.e., structure and composition) along gradients. An analysis of changes in wetland structure and composition longitudinally identified two hydrogeomorphic types and laterally delineated wetland boundaries. The wide–flat type had a wide (131.2 ± 50.4 m) wetland patch and a mean lateral slope of 0.008 ± 0.003, in contrast the narrow–deep type had a significantly smaller (80 ± 40.2 m) and steeper (0.048 ± 0.06) wetland patch. Changes in hydrogeomorphology had distinct effects on the species composition of the wetland. Facultative wetland species such as Sporobolus pyrimidalis and Ischaemum afrum were associated with the wide–flat type, while, the narrow–deep type was characterized by more obligate, flood dependent species such as Phragmites australis, Mariscus congestus, and Eriochloa meyeriana. Internally, the structure and composition of ephemeral wetlands on the northern plains of Kruger National Park were spatially heterogeneous and correlated to hydrogeomorphic conditions, that are identifiable when examined at the wetland scale. Results add knowledge to wetlands as sources of landscape heterogeneity and highlight how environmental variation can result in increases in wetland heterogeneity.     

Regional prediction of wetland degradation in South Africa

Wetland assessments in South Africa continue to be undertaken at the scale of individual wetlands, while ultimately a landscape assessment is required for broader regional planning. The aim of this research was to develop probability models of degradation per wetland type using landscape-scale predictor variables. Condition data for a total of 463 seep, floodplain and valley bottom (channelled and unchannelled) hydrogeomorphic (HGM) units was combined with data for 21 potential explanatory variables for land cover, infrastructure and catchment physiography. Multiple logistic regression models to estimate the probability of degradation per HGM type were investigated at three different spatial levels (1,000?m buffer radius; 100 and 1,000?km² scales). Models at the intermediate scale were most useful and only these are reported. Percent natural vegetation, road density, population density and altitude, together with anthropogenic land use (cultivation and forestry plantation area) were important predictors of wetland condition, and differed per HGM type. Regional patterns of degradation within quaternary catchments in KwaZulu-Natal were dissimilar for each HGM type. There is potential to refine and extend the models for application at a national level, and to predict actual condition scores using ordinal logistic regression based on larger datasets.     

Assessing the relationship between biomass and soil organic matter in created wetlands of central Pennsylvania, USA

Created wetlands are frequently structurally different from the natural wetlands they are intended to replace. With differences in structure might come differences in function. Most created wetlands in central Pennsylvania have very low amounts of soil organic matter relative to levels found in natural wetlands. However, anecdotal evidence also suggests that plant production is equivalent in created wetlands to natural wetlands. There is little evidence to indicate that this plant biomass in created wetlands is finding its way into the soil as organic matter. This might translate into a lack of function in the mitigation wetlands. To address this issue, we studied plant biomass production in seven created wetlands in central Pennsylvania (USA). We measured above- and below-ground biomass and compared results with known values of soil organic matter and hydrology for the same wetlands. We found biomass to be approximately equivalent to that produced in natural freshwater marshes, although the below-ground component was somewhat higher. We found no relationship of biomass to soil organic matter, even though site conditions were wet enough to retard plant decomposition.     

Changes of Soil Particle Size Distribution in Tidal Flats in the Yellow River Delta

Background

The tidal flat is one of the important components of coastal wetland systems in the Yellow River Delta (YRD). It can stabilize shorelines and protect coastal biodiversity. The erosion risk in tidal flats in coastal wetlands was seldom been studied. Characterizing changes of soil particle size distribution (PSD) is an important way to quantity soil erosion in tidal flats.

Method/Principal findings

Based on the fractal scale theory and network analysis, we determined the fractal characterizations (singular fractal dimension and multifractal dimension) soil PSD in a successional series of tidal flats in a coastal wetland in the YRD in eastern China. The results showed that the major soil texture was from silt loam to sandy loam. The values of fractal dimensions, ranging from 2.35 to 2.55, decreased from the low tidal flat to the high tidal flat. We also found that the percent of particles with size ranging between 0.4 and 126 μm was related with fractal dimensions. Tide played a great effort on soil PSD than vegetation by increasing soil organic matter (SOM) content and salinity in the coastal wetland in the YRD.

Conclusions/Significance

Tidal flats in coastal wetlands in the YRD, especially low tidal flats, are facing the risk of soil erosion. This study will be essential to provide a firm basis for the coast erosion control and assessment, as well as wetland ecosystem restoration.     

Carbon sequestration in freshwater wetlands in Costa Rica and Botswana

Tropical wetlands are typically productive ecosystems that can introduce large amounts of carbon into the soil. However, high temperatures and seasonal water availability can hinder the ability of wetland soils to sequester carbon efficiently. We determined the carbon sequestration rate of 12 wetland communities in four different tropical wetlands—an isolated depressional wetland in a rainforest, and a slow flowing rainforest swamp, a riverine flow-through wetland with a marked wet and dry season, a seasonal floodplain of an inland delta—with the intention of finding conditions that favor soil carbon accumulation in tropical wetlands. Triplicate soil cores were extracted in these communities and analyzed for total carbon content to determine the wetland soil carbon pool. We found that the humid tropic wetlands had greater carbon content (P ≤ 0.05) than the tropical dry ones (96.5 and 34.8 g C kg^?1, respectively). While the dry tropic wetlands had similar sequestration rates (63 ± 10 g Cm^?2 y^?1 on average), the humid tropic ones differed significantly (P < 0.001), with high rates in a slow-flowing slough (306 ± 77 g Cm^?2 y^?1) and low rates in a tropical rain forest depressional wetland (84 ± 23 g Cm^?2 y^?1). The carbon accumulating in all of these wetlands was mostly organic (92–100%). These results suggest the importance of differentiating between types of wetland communities and their hydrology when estimating overall rates at which tropical wetlands sequester carbon, and the need to include tropical wetland carbon sequestration in global carbon budgets.     

HGM: a call for model validation

The hydrogeomorphic (HGM) approach to wetland functional assessment has been in place for more than 20 years, yet most models developed to date have not been validated. Although HGM models are typically calibrated to a data set, we lack true validation efforts, especially as wetland scientists and managers continue to assert that measuring structure equates to an assessment of function. This paper is a call for a renewed effort at HGM validation in order to fully assure that we know when structure is measured we are also measuring function.     

Using the floristic quality concept to assess created and natural wetlands: Ecological and management implications

We applied the floristic quality index (FQI) to vegetation data collected across a chronosequence of created wetland (CW) sites in Virginia ranging in age from one to 15 years post-construction. At each site, we also applied FQI to a nearby forested reference wetland (REF). We tested the performance of the index against a selection of community metrics (species richness, diversity, evenness, percent native species) and site attributes (age, soil physiochemical variables). FQI performed better when non-native species (C-value = 0) were removed from the index, and also when calculated within rather than across vegetation layers. A modified, abundance-weighted FQI showed significant correlation with community and environmental variables in the CW herbaceous layer and REF herbaceous and shrub-sapling layers based on Canonical correspondence analysis (CCA) ordination output. These results suggest that a “natives only”, layer-based version of the index is most appropriate for our region, and an abundance-weighted FQI may be useful for assessing floristic quality in certain layers. The abundance-weighted format has the advantage of preserving the “heritage” aspect of the species conservatism concept while also entraining the “ecology” aspect of site assessment based on relative abundances of the inhabiting species. FQI did not successfully relate CW sites to REF sites, bringing into question the applicability of the FQI concept in comparing created wetlands to reference wetlands, and by analogy, the use of forested reference wetlands in general to assess vegetation development in created sites.     

The impact of anthropogenically induced degradation on the vegetation and biochemistry of South African palmiet wetlands

There are many different anthropogenic causes of wetland degradation, such as disturbances which affect the physical structure of wetlands, resulting in erosion (altered fire regimes, road and railway building through wetlands, channelization of wetlands), pollution, land-cover change, and climate change. These different types of degradation have various impacts, depending on the type of wetland, soils, biochemistry and other factors. We researched a poorly-studied South African valley-bottom peatland that is dominated by the ecosystem engineer Palmiet: Prionium serratum. We ask the question: what is the impact of degradation by gully erosion, pollution and alien tree invasion on biochemistry and plant community composition of palmiet wetlands? In 39 plots from three palmiet wetlands situated approximately 200 km apart we found that channel erosion, through a loss of alluvium, has probably resulted in leached soils with lower soil organic matter and water content, less able to retain nutrients and cations. Soil leaching is a possible explanation for the groundwater of degraded wetlands having higher electrical conductivity and pH than that of pristine wetlands and a lower soil cation exchange capacity (21.3?±?5.80–7.7?±?4.91 meq/100 g). The loss of alluvium typically resulted in a completely new plant community, composed mostly of pioneer species and several alien species. The increase in base saturation (17.5?±?8.46–30.2?±?17.85%) and soil pH (4.8?±?0.51–5.1?±?0.50) with degradation was hypothesized to be the result of liming practices. Once extremely degraded, i.e. all the alluvium is lost, it is unlikely that these sensitive palmiet wetlands will recover original vegetation communities and lost functions, except on long timescales. We recommend conservation of the few pristine wetlands that remain, and rehabilitation of those that still retain some of their original function.